J Mol Biol. 1988 Oct 20;203(4):949-59.
Mutations in the Tn10 tet repressor that interfere with induction. Location of the tetracycline-binding domain.

Smith LD, Bertrand KP.

Department of Microbiology and Molecular Genetics, University of California, Irvine 92717.

Tetracycline induces transcription of the Tn10 tetracycline resistance gene (tetA) by binding to the tet repressor, thereby reducing the repressor's affinity for two operator sites that overlap the tet promoters. We characterized mutations in the tet repressor (tetRs mutations) that interfere with induction of tetA expression. The mutations were isolated on multicopy Tn10 tet plasmids by selecting for resistance to the inducer 5a,6-anhydrotetracycline. Under these conditions, maximal induction of tetA expression inhibits the growth of Escherichia coli K-12. DNA sequence analysis of 25 spontaneous tetRs mutations identified amino acid changes at 13 different positions clustered near the middle of the 207 amino acid residue sequence of tet repressor. This region (residues 64 to 107) is distinct from the bihelical DNA-binding motif of tet repressor (residues 26 to 47). The capacity of tetRs repressors to bind tet operator DNA and to respond to inducer was examined in vivo in tetA-lacZ fusion strains. In three cases, the capacity of tetRs repressors to bind tetracycline was examined in vitro using cell extracts enriched in repressor. Mutations 64Y (His64----Tyr) and 82H (Asn82----His) reduce the repressor's affinity for tetracycline more than 1000-fold and more than 100-fold, respectively, suggesting that His64 and Asn82 may be part of the inducer-binding site or directly involved in maintaining its conformation. Mutation 103I (Thr103----Ile) reduces the repressor's affinity for tetracycline less than tenfold, yet it interferes with induction to a greater extent than either 64Y or 82H, suggesting that 103I may also reduce the repressor's capacity to undergo a conformational change required for induction. The properties of tetRs mutants suggest that the region of amino acid residues 64 to 107 is involved in inducer binding and in signalling between the inducer-binding and operator-binding domains of the repressor.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3062183&dopt=Abstract antibiotics, tetracycline

genetik.uni-bielefeld.de

The complete nucleotide sequence of the tetracycline resistance plasmid pAG1 from the gram-positive soil bacterium Corynebacterium glutamicum 22243 (formerly Corynebacterium melassecola 22243) was determined. The R-plasmid has a size of 19,751 bp and contains at least 18 complete open reading frames. The resistance determinant of pAG1 revealed homology to gram-negative tetracycline efflux and repressor systems of Tet classes A through J. The highest levels of amino acid sequence similarity were observed to the transmembrane tetracycline efflux protein TetA(A) and to the tetracycline repressor TetR(A) of transposon Tn1721 with 64 and 56% similarity, respectively. This is the first time a repressor-regulated tet gene has been found in gram-positive bacteria. A new class of tetracycline resistance and repressor proteins, termed TetA(Z) and TetR(Z), is proposed. Copyright 2000 Academic Press.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11078655&dopt=Abstract antibiotics, tetracycline




Antimicrob Agents Chemother. 1988 Dec;32(12):1797-800.
The cryptic tetracycline resistance determinant on Tn4400 mediates tetracycline degradation as well as tetracycline efflux.

Park BH, Levy SB.

Department of Molecular Biology, Tufts University School of Medicine, Boston, Massachusetts.

Escherichia coli containing the cryptic tetracycline resistance determinant (class F) from the Bacteroides fragilis transposon Tn4400 on plasmid pGAT400 expressed a detoxification of tetracycline as well as an active efflux of tetracycline. This finding concurs with the report of detoxification for a related tetracycline resistance determinant from B. fragilis on Tn4351 (B. S. Speer and A. Salyers, J. Bacteriol. 170:1423-1429, 1987), which specifies a 10-fold-higher resistance than Tn4400. Inactivation of tetracycline occurred at an initial rate of congruent to 0.7 micrograms of tetracycline per h per 10(8) cells, as determined by biologic assay and chromatographic analysis. The detoxification is a chemical degradation which can occur in the absence of energy-dependent efflux. The products of this degradation were not substrates for active transport into susceptible cells or out of pGAT400-containing E. coli. These results indicate that Tn4400 mediates two functionally different mechanisms for tetracycline resistance: an active efflux of tetracycline and a degradation of tetracycline.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3072922&dopt=Abstract antibiotics, tetracycline




Int J Clin Pharmacol Biopharm. 1977 Nov;15(11):542-6.
[Effect of chlortetracycline on the peptide spectrum of rat serum]

[Article in German]

Adam J, Barna K, Grega B.

Application of chlortetracycline in rats resulted in the occurence of certain peptides in the blood-serum, which could not be detected in the serum of an untreated control group. These results were obtained by means of high voltage electrophoresis and paper electrophoresis of the serum of rats which was analyzed 1,3, and 13 hours respectively after a single dose of 50 mg chlortetracycline per 100 g body weight in comparison to an untreated control group. The new peptides could be found in the slight alkaline range 1 and 3 hours after application of chlortetracycline and in the strong acidic area of the electrochromatogram 13 hours thereafter. A more detailed investigation of the new peptides could demonstrate that the number of the following amino acids was reduced in the peptide chains after chlortetracycline: leucine, valine, serine, arginine, and lysine. On the other hand, amino acids, such as citrulline, sarcosine, alpha-aminobutyric acid, and ornithine, could be found which are normally not present in proteins.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=591162&dopt=Abstract antibiotics, tetracycline




Mikrobiologiia. 1976 Nov-Dec;45(6):1049-55.
[Mechanism of bacterial resistance to tetracyclines and the importance of structural elements of tetracycline molecule for induction of resistance]

[Article in Russian]

Myl'nikova SI, Plakunov VK.

The resistance of Staphylococcus aureus P-282 and E. coli E-107 to chlorotetracycline is based on the acquired ability of energy-dependent "counteraction" with regard to penetration of the antibiotic in to the cells. Thus, inhibitors of energy processes stimulate chlorotetracycline absorption by resistant strains and increase their sensitivity to the antibiotic. The studied bacterial hospital strains absorb chlorotetracycline by means of oxalacetic acid transport system similar to resistant strains obtained in the laboratory. The transport system of chlorotetracycline is stereospecific and is involved in absorption of analogues of the antibiotic with the intact phenoldiketone or diphenol structure of the molecule. These analogues, like the natural antibiotic, induce an increase in the resistance to the antibiotic. No changes in the nature of the antibiotic transport system occur during induction. The increased resistance caused by induction is due entirely to a decrease in absorption of the antibiotic by the cells.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=796630&dopt=Abstract antibiotics, tetracycline




Chemotherapy. 1976;22(5):319-23.
Correlation of in vitro resistance of Staphylococcus aureus to tetracycline, doxycycline, and minocycline with in vivo use.

Lewis SA, Altemeier WA.

Susceptibility of 983 isolates of Staphyloccus aureus to tetracycline, doxycycline and minocycline was determined in vitro. Minocycline was shown to be more active than doxycycline, which in turn was shown to be slightly more active than tetracycline. 77% of the isolates which were resistant to tetracycline were also resistant to doxycycline, whereas only 4% of the tetracycline-resistant isolates were resistant to minocycline. The in vivo use of tetracycline correlated with increased in vitro resistance of S. aureus to tetracycline and doxycycline. A correlation between use of tetracycline and in vitro resistance to minocycline was not demonstrated.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=947710&dopt=Abstract antibiotics, tetracycline




Antimicrob Agents Chemother. 1993 Dec;37(12):2699-705.
A new tetracycline resistance determinant, Tet H, from Pasteurella multocida specifying active efflux of tetracycline.

Hansen LM, McMurry LM, Levy SB, Hirsh DC.

Department of Veterinary Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis 95616.

The tetracycline resistance determinant on plasmid pVM111 from an avian strain of Pasteurella multocida mediates tetracycline resistance by a regulated active efflux mechanism. DNA coding for the determinant did not hybridize at high stringency with DNA representing a group of common tetracycline resistance determinants. The DNA sequence, however; revealed a structural gene and a repressor gene which had significant (37 to 64%) sequence similarities with previously described classes of efflux-type tetracycline resistance genes from members of the family Enterobacteriaceae. The new determinant has been assigned to class H.

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J Med Microbiol. 2000 May;49(5):415-8.
Primary and combined resistance to four antimicrobial agents in Helicobacter pylori in Sofia, Bulgaria.

Boyanova L, Stancheva I, Spassova Z, Katzarov N, Mitov I, Koumanova R.

Department of Microbiology, Medical University, Sofia, Bulgaria.

The aim of this study was to evaluate the primary and combined resistance of Helicobacter pylori against four antimicrobial agents by a screening agar method (SAM) and a modified disk diffusion method (MDDM) alone and in combination. Pre-treatment H. pylori isolates from 192 consecutive H. pylori-positive patients at three hospitals in Sofia were investigated. MDDM was performed with disks containing metronidazole (5 microg), clarithromycin (15 microg) or erythromycin (15 microg), ciprofloxacin (5 microg) and tetracycline (30 microg). Resistance was determined by an inhibitory zone of <16 mm for metronidazole and < or =30 mm for other agents tested. The cut-off concentrations used to define resistance by SAM were: metronidazole >8 mg/L, clarithromycin >2 mg/L, tetracycline >4 mg/L and ciprofloxacin >1 mg/L. Primary resistance rates in H. pylori were: metronidazole 28.6%, clarithromycin 9.7%, metronidazole + clarithromycin 2.8%, ciprofloxacin 3.9%, metronidazole + ciprofloxacin 2.3%, tetracycline 1.9% and metronidazole + tetracycline 1.2%. Among metronidazole-resistant isolates, combined resistance to clarithromycin, ciprofloxacin and tetracycline was present in 11.4% (5 of 44 strains), 8.3% (3 of 36) and 4.9% (2 of 41), respectively. Two strains exhibited triple resistance to macrolides, metronidazole and either ciprofloxacin or tetracycline. Three tetracycline-resistant strains were detected in 1999; however, resistance rates to other agents were relatively stable during the 6 years. Primary H. pylori resistance to metronidazole is moderate and resistance to clarithromycin and to ciprofloxacin is considerable in comparison with results in most other countries. The alarming appearance of strains harbouring combined resistance or multiresistance provides the motivation for continued surveillance of H. pylori at global, national and regional levels.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10798553&dopt=Abstract antibiotics, tetracycline